Electron discharge device



Patented May 16, 1939 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Delaware Application March 27, 1937, Serial No. 133,300

8 Claims.

My invention relates to electron discharge devices, more particularly to improvements in such devices having a gaseous atmosphere and capable of being continuously controlled.

In the conventional grid controlled vacuum tubes provided with a. thermionic cathode, control grid and anode, the space charge which builds up around the cathode makes necessary the use of comparatively high voltages, such as 100 volts or more, for obtaining current sufficiently large for practical purposes. It is also necessary to use comparatively large grid voltage swings to produce usable variations in the output of the tube. Thus, in the conventional high vacuum. tubes comparatively large transconductances are not easily obtainable nor can large anode currents be obtained with small anode voltages. It has been recognized that by introducing a gas in a tube and ionizing the gas the space charge around the cathode could be neutralized and thus large anode currents obtained with the usual anode voltages. However, in the conventional grid controlled tube containing gas, ionization of the gas causes the control grid to lose its control of the electron stream so that while initiation of ionization can be controlled the current cannot be controlled by the control electrode after ionization takes place. Furthermore, in these types of tubes comparatively high voltages, much above ionization voltages, are applied between the anode and cathode to cause a gas discharge between the anode and the cathode. Thus while comparatively high currents can be obtained the loss of grid control and the necessity for high anode-cathode voltages limits the application of this type of tube and prevents its use in conventional radio circuits.

It is the principal object of my invention to provide an improved electron discharge device of the gas type in which a small amount of input power to the device is capable of controlling with small anode voltages and small control grid voltage swings large amounts of power in the output of the device. More specifically it is an object of my invention to provide such a gas tube depending upon gas ionization for its operation but which nevertheless can be continuously controlled.

In accordance with my invention I produce such a tube by introducing gas at a low pressure into an envelope containing the electrodes and ionizing the space between the cathode and the anode to neutralize the space charge and thus make available a large number of electrons. I can then apply only a very small voltage of the order of 6 volts, for example, which is considerably below ionizing voltage between the anode and cathode to obtain a comparatively large anode current. The flow of electrons from the cathode to the anode can then be continuously controlled by an electrode to which is applied comparatively small voltage swings inasmuch as there is no gas discharge between the main cathode and the anode. To produce the ionization of the gas between the cathode and anode I may employ an auxiliary cathode and establish a discharge between this auxiliary cathode and another electrode, the electrode being so positioned that the space between the main cathode and the anode is positioned in the vicinity of the auxiliary discharge between the auxiliary cathode and its cooperating electrode.

In one preferred embodiment of my invention I mount within an envelope containing gas at low pressure, a straight indirectly heated cathode surrounded by a cylindrical anode closed at both ends. An aperture, preferably covered by.

a mesh material, is provided at one end of the anode. Registering with this aperture are a control grid and an auxiliary cathode for supplying the electrons within the anode to ionize the gas around the cathode within the anode. The auxiliary cathode, grid and the aperture covered by mesh material are all spaced less than the mean free path of electrons in the gas so that no ionization takes place between these electrodes. This arrangement permits continuous grid control of the ionization within the main anode. A voltage less than that required to produce ionization is applied between the main cathode and the main anode. A voltage sufliciently high to cause the electrons to have a great enough velocity in entering the space between the main cathode and the main anode is applied between the auxiliary cathode and the main anode, the control voltage being applied through an input circuit to the control grid.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a vertical section in perspective of an electron discharge device made according to my invention, Figure 2 is a section along 2-2 of Figure 1 showing details of construction, Figure 3 is a diagrammatic showing of a tube and circuit made according to my invention, and Figure 4 is a diagrammatic showing of a direct current amplifier arrangement using a tube made accord ing to my invention.

A tube made according to my invention and shown in Figure 1 includes an envelope i6 containing a gas at low pressure for example between 159-600 microns pressure. Heliurn at pressures between 250 and 300 microns is very satisfactory. A stem ii supports the electrode mount assembly within the envelope. In accordance with my invention the electrode mount assembly comprises an indirectly heated cathode l2 enclosed within a cylindrical anode l3 provided with a screen covered aperture i4 and closed ends l5 and I6. Aperture i4 is to provide a gas communication between the interior of the anode and the inside of the envelope. The cathode i2 is insulatingly supported from the upper closed end I6 of the anode by means of the insulating bushing ll. The lower end I5 is provided with an ap- 20,erture |8 covered with foraminous or mesh material l8, the shape of this aperture being best shown in Figure 2. The cathode |2 and anode l3 are the main discharge electrodes between which the output current passes.

In order to neutralize the space charge around the cathode |2 during operation of the tube I provide an auxiliary electrode system comprising an indirectly heated cathode and grid in registry with the aperture |8 to project electrons from the auxiliary cathode into the space surrounding the cathode l2.

This electrode system comprises an indirectly heated auxiliary cathode l9 supported and electrically connected to the metal disc 20. Insulatingly separated from the disc 2|! by means of an insulating disc member 2| having an aperture 22, in which the cathode I9 is positioned, is a grid comprising a metallic disc member 23 having an aperture 24 covered with a mesh material 24, this aperture being in registry with the aperture It! in the lower end of the anode. This grid is insulatingly separated from the anode by means of the insulating disc 25 having an aperture 26 in registry with the aperture l8. This whole mount assembly is supported from the stem H by means of the supports and leads 21, 28 and 28 connected respectively to the cathode disc, grid disc and anode. The main cathode I2 is provided with a lead 30.

In operation a low voltage less than that required for maintaining ionization is applied between the main cathode l2 and anode I3 so that a gas discharge cannot take place between these electrodes. Voltages are applied between the auxiliary cathode I9 and the anode l3, which are high enough to cause electrons from the cathode to be projected through the aligned apertures into the space around the cathode l2 with sufficient velocity to ionize the gas and thus neutralize the space charge. The grid 23 may have applied to it a control voltage which will control the flow of electrons from the auxiliary cathode I9 into the space surrounding the main cathode l2 to thereby control the ionization and hence the current from cathode l2 to anode l3.

A circuit employing a tube containing helium and made according to my invention, as shown in Figure 3, includes an input circuit comprising a source of varying voltage 3| and biasing battery 32 of about 4 volts connected between the control grid 23 and the auxiliary cathode IS. .The output circuit includes the primary of the transformer 34 and biasing battery 35 of the order of 6 volts which provides a low voltage connected between the main cathode l2 and anode l3. A

source of voltage supply 33 which may be between 50 to 100 volts, preferably about 70 volts, for helium is connected between auxiliary cathode is and anode l3 so that electrons leaving the cathode l9 will be projected into the space around the cathode i2 with sufficient velocity to cause ionization and hence neutralization of the space charge around the cathode The input or control voltage applied to the input inductance 3| controls the ionization and hence the current flowing in the output of the tube. Since the ionization is entirely dependent upon the electrons from the auxiliary cathode i9, the voltage between the main cathode |2 and the main anode |3 being too low to maintain a gaseous discharge even though there is ionization, the current be tween the cathode l2 and anode I3 is determined substantially entirely by the voltage applied to the control grid 23. Because of the close spacing between grid 23, cathode I9 and anode l8, which is of the order of the mean-free-path of an electron in the gas, continuous grid control over the electron stream from the auxiliary cathode is maintained since ionization cannot take place between these electrodes to cause loss of grid control. In this way very small voltages applied to the control grid control large currents between the main cathode and the main anode resulting in a tube having high transconductance and continuous grid control, although making use of a gaseous atmosphere.

One of the novel applications of a tube made according to my invention is to a D. C. amplifier comprising a self-excited oscillating circuit which can be used to provide a high voltage D. C. output source from a low voltage D. C. source. In Figure 4 the cathode I2 is connected through the low voltageD. C. source or battery to one side of the inductance 4|, the other side of which is connected through an output resistor 42 to the auxiliary cathode IS. The voltage obtained from battery 40 is less than that required to maintain ionization between cathode I2 and anode l3. An intermediate point of the inductance 4| is connected by means of conductor 43 to the anode Hi. The grid 23 may be connected to the cathode. A condenser 44 connected across a part of the inductance 4| furnishes with the inductance 4| an oscillating circuit. The output resistor 42 is shunted by a filter condenser 45. In order to start oscillations a resistance 46 and switch 41 is provided.

To shock the system into operation switch 41 is momentarily closed causing a flow of current through the right hand portion of inductance 4|, which in turn induces a voltage across the left hand portion of inductance 4| and condenser 44. This voltage which is stepped up by proper ratio of turns of the two portions of inductance 4| is applied between the cathode l9 and the anode l3 and causes electrons to discharge into the space surrounding the cathode l2 causing ionization which neutralizes the space charge thereby permitting a large flow of current between the cathode I2 and anode I3. This current flowinc' through the right hand portion of the inductance 4| again feeds back energy to the left hand portion producing a regenerative action so that the system is maintained in oscillation. Due to the rectifying action between the cathode |9 and anode I8, rectified voltages appear across the output resistance 42, the condenser acting as a filter so that substantially uniform D. C. voltage appears across this output circuit comprising resistor 42 and condenser 45. By proper circuit constants a step-up voltage can be provided across the D. 0. output terminals.

While I have indicated the preferred embodiment 01' my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact iorms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is- 1. An electron discharge device having an envelope containing a gas, a thermionic cathode within said envelope for emitting electrons, a hollow anode surrounding said thermionic cathode i'or enclosing the space between said thermionic cathode and said anode. means for applying a voltage between said thermionic cathode and anode less than that required for maintaining ionization between said thermionic cathode and anode, and means for ionizing the space between said thermionic cathode and anode and including an auxiliary cathode and an auxiliary electrode through which electrons from said auxiliary cathode can pass into the space between said thermionic cathode and said anode, means for applying a voltage between said auxiliary cathode and said anode for causing electrons to be projected with sufllcient velocity into the space between said thermionic cathode and said anode to ionize the gas between said thermionic cathode and anode.

2. An electron discharge device comprising an envelope containing a gas, a thermionic cathode within said envelope, a hollow anode surrounding said cathode to enclose the space between said thermionic cathode and said anode, and having an aperture provided in said hollow anode, means for applying a voltage between said thermionic cathode and anode less than that required for maintaining ionization of the gas between said thermionic cathode and anode, an auxiliary cathode positioned in registry with said aperture and means for applying a voltage between said auxiliary cathode and the anode for causing electrons from said auxiliary cathode to pass through said aperture with sufilcient velocity to ionize the gas between said thermionic cathode and anode.

3. An electron discharge device comprising an envelope containing a gas at low pressure, a thermionic cathode within said envelope, an anode surrounding said cathode to completely enclose the space between the cathode and anode, means for applying a voltage between said cathode and anode less than that required for ionization of the gas between said thermionic cathode and anode, said anode having an aperture therein, an auxiliary cathode in registry with said aperture, means for applying a voltage applied between said auxiliary cathode and said anode for causing electrons to pass through said aperture in said anode with suificient velocity to ionize the gas between the thermionic cathode and anode, and means for confining electrons from said auxiliary cathode so that the electrons can pass only through the aperture in said anode.

4. An electron discharge device comprising an envelope containing a gas at low pressure, a thermionic cathode within said envelope, an anode surrounding said thermionic cathode to completely enclose the space between said thermionic cathode and anode, said anode having an aperture therein, an auxiliary cathode in registry with said aperture for providing electrons which pass-through said aperture in said anode to ionize the gas between the thermionic cathode and anode, means for confining electrons from said auxiliary cathode so that the electrons can pass only through the aperture in said anode, and a grid electrode positioned between said aperture and said auxiliary cathode.

5. An electron discharge device having an envelope containing gas at a low pressure, a straight thermionic cathode within said envelope, a cylindrical anode coaxial with and surrounding said cathode and having closed ends for completely enclosing the space between said cathode and said anode, one 01' said ends being provided with a foraminated aperture, a grid and auxiliary cathode in registry with said aperture, means for applying a voltage between said thermionic cathode and anode less than that required to maintain ionization between said thermionic cathode and anode, means for applying a voltage between said auxiliary cathode and anode to cause electrons from said auxiliary cathode to pass through said foraminated aperture with suflicient velocity to ionize the gas in the space between the thermionic cathode and anode, means for applying a control voltage between said grid and the auxiliary cathode for controlling said ionization.

6. An electron discharge device comprising an envelope containing a. gas at a low pressure, a straight thermionic cathode within said envelope, a tubular anode having closed ends coaxial with and surrounding said cathode for enclosing the space between said thermionic cathode and said anode, one of said closed ends being provided with a foraminated aperture, a control electrode and an auxiliary cathode in registry with said aperture, and a sheet of insulating material on each side of said control electrode for separating said control electrode from the closed end of said anode and said auxiliary cathode, each of said sheets being provided with an aperture in registry with the aperture in said anode.

7. An electron discharge device comprising an envelope containing a gas at a low pressure, a straight thermionic cathode within said envelope, a tubular anode having closed ends coaxial with and surrounding said cathode for enclosing the space between said thermionic cathode and anode, one of said closed ends being provided with an aperture, a control electrode adjacent the end of said anode provided with said aperture, a sheet of insulating material between said control electrode and said anode and having an aperture in registry with the aperture in said anode, an auxiliary cathode positioned adjacent said grid and insulatingly supported adiacent said control electrode, in registry with the aperture in said anode.

I 8. An electron discharge device comprising an envelope containing a gas at a low pressure, a straight thermionic cathode within said envelope, a tubular anode having closed ends coaxial with and surrounding said cathode forenclosing the space between said thermionic cathode and anode, one of said closed ends being provided with 10 anode, an auxiliary cathode positioned adjacent said grid and insulatingly supported adjacent said control electrode in registry with the aperture in said anode, means for applying a voltage between said anode and thermionic cathode less than that required to maintain ionization between said thermionic cathode and said anode, means for applying a voltage between said auxiliary cathode and said anode sufficiently great o to cause electrons from the auxiliary cathode to areas 

